Seamless mode does not work across multiple monitors

Description

Virtualbox running on a Windows XP host, will not display guest windows in seamless mode on secondary monitors. When the virtualbox guest is in a secondary monitor and seamless mode is switched on, the guest will disappear entirely. When seamless mode is switched on the primary monitor, guest windows cannot be dragged to other displays.

A proposed solution:
Render the guest windows inside of native host windows. Treat each guest window like a native application. This is how Xming and Microsoft RemoteApp does seamless rdp. Doing this will solve many other rendering issues (like background windows overlapping the host task bar).